Streaming is one of the methods of receiving a content such as audio and video from a server and reproducing such content. Streaming is used in the case where the size of a content is large and thus it takes time if its reproduction is started after the whole content is downloaded and where a copyrighted content which cannot be stored in a reproduction device is reproduced, but a communication path is required to be stable.
In a wireless communication in a moving body, the state of communication changes owing to various conditions such as the present position of the moving body, and it happens in an extreme case that no communication can be carried out at all. Against this backdrop, there is a communication device equipped with plural communication means so that it is possible to perform transmission and reception using one of such communication means that is selected depending on the present circumstances and a condition requested by a user (for example, refer to Patent Document 1).
FIG. 1 is a block diagram showing the structure of a conventional communication device described in Patent Document 1.
As shown in FIG. 1, such conventional communication device 900 is comprised of: a present position detector 901; a speed sensor 902; an input device 903; a controller 904; a display device 905; a DSRC device 906; a middle range device 907; a stationary satellite device 908; a cellular phone device 909; and a low orbit satellite device 910.
The present position detector 901 is connected to the controller 904, and a communication means available at the present position is selected from among plural communication means such as the DSRC device 906 and the cellular phone device 909, using a database 904a. Furthermore, the use order of the communication means is determined based on a condition requested by the user, such as communication charge and communication speed. Then, the communication means are used one by one according to such determined order and a communication is carried out using the communication means by which a communication was first carried out successfully.    Patent Document 1: Japanese Laid-Open Patent Application No. 2000-175249 (pp. 1-8, FIG. 1)
However, since the above-described on-board communication device uses only one communication means at one time, there is a problem that streaming reproduction of a content cannot be carried out properly because of insufficient transmission speed that happens in the case where the transmission speed has changed due to a change in the position of the moving body and where the maximum value of the transmission speed of one communication means is less than the rate assigned to the content for streaming.
The present invention aims at solving the above conventional problem, and it is an object of the present invention to provide a content transmission device and a content reproduction device that realize streaming reproduction in an environment in which an effective communication speed changes due to a change in the position of a moving body such as a vehicle.